Lab Manual Exercise #10D
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Photos Of Ecological Adaptations #2

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Photos Of Ecological Adaptations #1

Table Of Contents:

    1.   Camouflage (Cryptic)   
    2.   Disruptive Markings       
    3.   Warning Coloration       
    3.   Mating Coloration       
    5.   Batesian Mimicry       
    6.   Automimicry       
    7.   Xerarch Succession
    8.   Hydrarch Succession
    9.   Forest Succession
  10.   Retrogression
  11.   Major Biomes of N. America

7. Xerarch Succession

Xerarch Succession: Plant succession starting on bare ground or rock and culminating in a mature climax forest. The pioneer species, such as lichens and mosses, result in the gradual accumulation of soil. Forested slopes in the Sierra Nevada (Yosemite National Park) were once bare granite after the last major glacial period 12,000 years ago. Today these slopes contain dense forests of lodgepole pine (Pinus contorta), red fir (Abies magnifica) and mountain hemlock (Tsuga mertensiana). If you probe down through the thick layers of duff (needles, leaves, cone scales & branchlets) and soil, you will encounter a bedrock of solid granite.

The lichen colonies on these boulders are the first step in xerarch succession. Along with mosses, they trap dust particles and form a layer of soil on the rock surface that allows other plants, such as grasses and herbs, to become established.

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8. Hydrarch Succession

Hydrarch: Plant succession starting on relatively shallow water, such as ponds and lakes, and culminating in a mature forest.

Four stages of hydrarch succession: 1. Submersed aquatic plants in the deeper water. 2. Emergent cattails and bulrushes rooted in the mud of shallow water. 3. Willow thickets along the banks of distant shoreline. 4. Conifer forest in drier, well drained soil above the willow thickets.

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A pristine pond in the alpine Sierra Nevada. Grasses and sedges are now encroaching on the pond. In time, depending on local geological and climatological conditions, this pond may gradually turn into a meadow.

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9. Forest Succession

Pioneer Trees: Early stage in forest succession in which the seedling and sapling trees are shade intolerant and must have full sunlight to survive. The pioneer forest cannot perpetuate itself because its seeds fall into the shady understory of parental trees where the seedlings cannot survive. Examples of pioneer trees are the lodgepole pines (Pinus contorta ssp. murrayana) in the Sierra Nevada and Pinus contorta ssp. latifolia) in the Rocky Mountains, and the Douglas fir (Pseudotsuga menziesii) in the Pacific northwest.

Climax Trees: The final stage of succession in a given region where the vegetation type is able to perpetuate itself. Climax trees are shade tolerant and able to develop from seedlings in the shady understory of parental trees. Examples of climax trees are the Engelmann spruce (Picea engelmannii) in the Rocky Mountains and western hemlock (Tsuga heterophylla) in the Pacific northwest. Climax forest trees in the local mountains of San Diego County include the white fir (Abies concolor) and incense cedar (Calocedrus decurrens).

Left: Forest succession in the Rocky Mountains of Colorado showing a pioneer forest of lodgepole pine (Pinus contorta ssp. latifolia) with small, shade tolerant Engelmann spruce (Picea engelmannii) in the understory. Eventually the lodgepole pines may be replaced by a climax forest of Engelmann spruce. A forest fire could result in retrogression and return this area to pioneer conditions (bare ground and ash) which would favor the shade intolerant lodgepole pines. Right: Several mature lodgepole pines (Pinus contorta ssp. murrayana) in the Sierra Nevada with smaller individuals of red fir (Abies magnifica var. magnifica) in the understory. Lodgepole seedlings cannot survive in the shade of the parental trees and in the thick layer of duff (red arrow) beneath the trees. The duff layer is composed of dead needle leaves, branchlets and cone scales. In time (centuries) these young red firs may replace the lodgepole pines.

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A subalpine meadow in the Sierra Nevada under invasion by lodgepole pines (Pinus contorta ssp. murrayana). Depending upon local geological and climatolgical conditions, this area of grasses and sedges may eventually be replaced by a forest of lodgepole pines.

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10. Retrogression

Retrogression: This dense marsh was completely washed away by a flash flood that roared down the canyon. Click on the photo to see the same area after the flood.

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Retrogression: A phenomenon where succession reverts back to pioneer conditions, such as water or bare ground. Examples of retrogression are flood waters, fire and volcanic eruptions. Retrogression occurred on the slopes surrounding Mount St. Helens in southern Washington when the forest was reduced to bare ground.

Retrogression on Mount Lassen in northern California. During 1914-1915 this ancient volcano erupted. Hot gasses, molten lava and ash melted the snow-covered summit and an enormous mud slide came down the steep slopes, wiping out the forest in its path. The trees (including lodgepole pine) have reseeded the barren slopes and the forest is slowly growing back.

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